Abstract not found

Personal servers are an attractive concept: People carry around a device that takes care of computing, storage and communication on their behalf in a pervasive computing environment. So far personal servers have mainly been considered for accessing personal information. In this paper, we consider personal servers in the context of a digital key system. Digital keys are an interesting alternative to physical keys for mail or good delivery companies whose employees access tens of private buildings every day. In this paper, we present a digital key system tailored for the current incarnation of personal servers, i.e., a Bluetooth-enabled mobile phone. We describe how to use Bluetooth for this application, we present a simple authentication protocol and we provide a detailled analysis of response time and energy consumption on the mobile phone.

Abstract—Message delivery in sparse mobile ad hoc networks (MANETs) is difficult due to the fact that the network graph is rarely (if ever) connected. A key challenge is to find a route that can provide good delivery performance and low end-to-end delay in a disconnected network graph where nodes may move freely. We cast this challenge as an information flow problem in a social network. This paper presents social network analysis metrics that may be used to support a novel and practical forwarding solution to provide efficient message delivery in disconnected delay-tolerant MANETs. These metrics are based on social analysis of a node’s past interactions and consists of three locally evaluated components: a node’s “betweenness ” centrality (calculated using ego networks), a node’s social “similarity ” to the destination node, and a node’s tie strength relationship with the destination node. We present simulations using three real trace data sets to demonstrate that by combining these metrics delivery performance may be achieved close to Epidemic Routing but with significantly reduced overhead. Additionally, we show improved performance when compared to PRoPHET Routing. Index Terms—Delay- and disruption-tolerant networks, MANETs, sparse networks, ego networks, social network analysis.

In recent studies, using mobile elements (MEs) as mechanical carriers of data has been shown to be an effective way of prolonging sensor network life time and relaying information in partitioned networks. As the data generation rates of sensors may vary, some sensors need to be visited more frequently than others. In this paper, a partitioning-based algorithm is presented that schedules the movements of MEs in a sensor network such that there is no data loss due to buffer overflow. Simulation results show that the proposed Partitioning Based Scheduling (PBS) algorithm performs well in terms of reducing the minimum required ME speed to prevent data loss, providing high predictability in inter-visit durations, and minimizing the data loss rate for the cases when the ME is constrained to move slower than the minimum required ME speed.

Abstract not found

Abstract — Our problem formulation is as follows. Given a probabilistic graph G and routing algorithm A, we wish to determine a delivery subgraph G[A] of G with at most k edges, such that the probability Conn2(G[A]) that there is a path from source s to destination t in a graph H chosen randomly from the probability space defined by G[A] is maximized. To the best of our knowledge, this problem and its complexity has not been addressed in the literature. Also, there is the corresponding distributed version of the problem where the delivery subgraph G[A] is to be constructed distributively, yielding a routing protocol. Our proposed solution to this routing problem is multi-fold: First, we prove the hardness of our optimization problem of finding a delivery subgraph that maximizes the delivery probability and discuss the hardness of computing the objective function Conn2(G[A]) (which is not the hardness of Conn2(G[A]) itself); Second, we present an algorithm to approximate Conn2(G[A]) and compare it with an optimal algorithm; Third, we model mobility using a Semi-Markov Chain to estimate the pairwise user contact probabilities; and Fourth, we propose an edgeconstrained routing protocol (EC-SOLAR-KSP) for intermittently connected networks based on the insights obtained from the first step and the contact probabilities computed in the third step. We then highlight the protocol’s novelty and effectiveness by comparing it with a probabilistic routing protocol, and an epidemic routing protocol proposed in literature for intermittently connected networks. I.

... (ICN) is a challenging problem due to the uncertainty and time varying nature of network connectivity. In this work, we focus on a special class of ICN formed by mobile ad hoc users called ICMAN. We first consider a new and practical probabilistic mobility model where the nodes move between a set of “hubs ” in a partially repetitive and nondeterministic pattern to form the so-called “sociological orbits”. Second, to leverage the sociological orbit based mobility pattern in routing within ICMAN, we propose a series of multi-path Sociological Orbit aware Location Approximation and Routing (SOLAR) protocols. We present theoretical analysis of the mobility model and routing algorithms under consideration, and show that the proposed routing algorithms can outperform other conventional routing approaches in an ICN by taking advantage of the sociological orbit based mobility pattern.

Abstract — Personal communication devices are increasingly equipped with sensors which are able to passively sample their surroundings. We envision a service that enables a community of users carrying such memory-limited devices to query the condition of various locations in the field in which they collectively roam. We show that existing techniques that rely on directed placement and retrieval (DPR), are viable approaches to implementing such a service, but only when the underlying network is well connected. Alternatively, we propose the use of amorphous placement and retrieval (APR), in which a cache management scheme is employed to store sensory samples locally, and an informed exchange of cached samples is used to diffuse the sensory data throughout the network, in such a way that the answer to any query (targeting an arbitrary location in the field) is likely to be found close to the query origin. A salient characteristic in such a setting is the relationship between the probability of roaming a location in the field and the probability of querying that location. If roaming and query probability distributions do not match—which is the case in many settings—then an important determinant of the performance of APR is the manner with which cached field samples are collectively shared and managed. In that regard, we argue that knowledge of the distribution of query targets could be used effectively by an informed cache management policy to maximize the utility of collective storage of all devices. Using a simple analytical model, we show that the use of informed cache management is particularly important when the mobility model results in a non-uniform distribution of users over the field. We present results from extensive simulations which show that in sparsely-connected networks, APR is more cost-effective than DPR, that it provides extra resilience to node failure and packet losses, and that its use of informed cache management yields superior performance.

Abstract—Personal communication devices are increasingly equipped with sensors for passive monitoring of encounters and surroundings. We envision the emergence of services that enable a community of mobile users carrying such resource-limited devices to query such information at remote locations in the field in which they collectively roam. One approach to implement such a service is directed placement and retrieval (DPR), whereby readings/queries about a specific location are routed to a node responsible for that location. In a mobile, potentially sparse setting, where end-to-end paths are unavailable, DPR is not an attractive solution as it would require the use of delay-tolerant (flooding-based store-carry-forward) routing of both readings and queries, which is inappropriate for applications with data freshness constraints, and which is incompatible with stringent device power/memory constraints. Alternatively, we propose the use of amorphous placement and retrieval (APR), in which routing and field monitoring are integrated through the use of a cache management scheme coupled with an informed exchange of cached samples to diffuse sensory data throughout the network, in such a way that a query answer is likely to be found close to the query origin. We argue that knowledge of the distribution of query targets could be used effectively by an informed cache management policy to maximize the utility of collective storage of all devices. Using a simple analytical model, we show that the use of informed cache management is particularly important when the mobility model results in a non-uniform distribution of users over the field. We present results from extensive simulations which show that in sparsely-connected networks, APR is more cost-effective than DPR, that it provides extra resilience to node failure and packet losses, and that its use of informed cache management yields superior performance.

Wireless sensor networks (WSNs) consist of large populations of wirelessly connected nodes, capable of computation, communication, and sensing. Sensor nodes cooperate in order to merge individual sensor readings into a high-level sensing result, such as integrating a time series of position measurements into a velocity estimate. The physical time of sensor readings is a key element in this process called data fusion. Hence, time synchronization is a crucial component of WSNs. We argue that time synchronization schemes developed for traditional networks such as NTP [21] are ill-suited for WSNs and suggest more appropriate approaches.